Janet Kwasniak's blog on consciousness and the brain

Unconscious effects

There is an interesting item in ScienceDaily (here) on the effect of perceptions that we are not conscious of. We can perceive an object, understand its meaning, and have that meaning affect our behavior, without any conscious awareness of the object. The paper’s lead author, Cacciamani, says, “Every day our visual systems are bombarded with more information than we can consciously be aware of. We’re showing that your brain might still be accessing information without your conscious awareness, and that could influence your behavior.”

The researchers use the way we perceive the figure and ground of a silhouette. We perceive the figure before we perceive the ground and we perceive the semantic meaning of the figure before the ground – in many cases we do not seem to be concerned at all about the meaning of the ground. They showed a silhouette for 50 milliseconds before a test, and did not tell the subjects to do anything with the image. The subjects were not aware that the ground suggested a particular meaning. As in the image, where the figure is meaningless and the ground suggests leaves, the leaves do not reach awareness in the short exposure.

The test was that subjects were shown an object and had to indicate whether it was natural or man-made. Before each test object, the short exposure to the silhouette was shown. “We found that participants performed better on the natural/artificial word task when that word followed a silhouette whose ground contained an object of the same rather than a different category.”

So although the subjects had no consciousness of meaningful objects in the ground, they were affected by the meanings. The perceptions of the ground-objects were complete and they were assigned meanings without conscious awareness. The meanings affected the choice of actions without conscious awareness. To me this indicates that perception, meaning, and decision are not necessarily always exclusively bound to consciousness.

Traditional theories of vision assume that figures and grounds are assigned early in processing, with semantics being accessed later and only by figures, not by grounds. We tested this assumption by showing observers novel silhouettes with borders that suggested familiar objects on their ground side. The ground appeared shapeless near the figure’s borders; the familiar objects suggested there were not consciously perceived. Participants’ task was to categorize words shown immediately after the silhouettes as naming natural versus artificial objects. The words named objects from the same or from a different superordinate category as the familiar objects suggested in the silhouette ground. In Experiment 1, participants categorized words faster when they followed silhouettes suggesting upright familiar objects from the same rather than a different category on their ground sides, whereas no category differences were observed for inverted silhouettes. This is the first study to show unequivocally that, contrary to traditional assumptions, semantics are accessed for objects that might be perceived on the side of a border that will ultimately be perceived as a shapeless ground. Moreover, although the competition for figural status results in suppression of the shape of the losing contender, its semantics are not suppressed. In Experiment 2, we used longer silhouette-to-word stimulus onset asynchronies to test whether semantics would be suppressed later in time, as might occur if semantics were accessed later than shape memories. No evidence of semantic suppression was observed; indeed, semantic activation of the objects suggested on the ground side of a border appeared to be short-lived. Implications for feedforward versus dynamical interactive theories of object perception are discussed.